Method for making a lithographic printing plate

ABSTRACT

A method for making a lithographic printing plate includes the steps of: (1) providing a heat-sensitive lithographic printing plate precursor including on a support having a hydrophilic surface or which is provided with a hydrophilic layer, a heat-sensitive coating, (2) image-wise exposing the precursor with IR-radiation or heat, and (3) developing the image-wise exposed precursor with an alkaline developing solution including a compound having at least two onium groups. According to the above method, a printing plate is formed with an improved developing latitude or an improved exposure latitude.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage Application ofPCT/EP2007/052443, filed Mar. 15, 2007. This application claims thebenefit of U.S. Provisional Application No. 60/784,414, filed Mar. 21,2006, which is incorporated by reference herein in its entirety. Inaddition, this application claims the benefit of European ApplicationNo. 06111310.6, filed Mar. 17, 2006, which is also incorporated byreference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for making a lithographicprinting plate wherein an image-wise exposed precursor is developed withan alkaline developing solution including a compound having at least twoonium groups. The present invention relates also to an alkalinedeveloping solution and to a replenishing solution including thecompound having at least two onium groups. The present invention relatesalso to a lithographic printing plate precursor wherein the coatingincludes the compound having at least two onium groups.

2. Description of the Related Art

Lithographic printing typically involves the use of a so-called printingmaster such as a printing plate which is mounted on a cylinder of arotary printing press. The master carries a lithographic image on itssurface and a print is obtained by applying ink to the image and thentransferring the ink from the master onto a receiver material, which istypically paper. In conventional lithographic printing, ink as well asan aqueous fountain solution (also called dampening liquid) are suppliedto the lithographic image which consists of oleophilic (or hydrophobic,i.e., ink-accepting, water-repelling) areas as well as hydrophilic (oroleophobic, i.e., water-accepting, ink-repelling) areas. In so-calleddriographic printing, the lithographic image consists of ink-acceptingand ink-adhesive (ink-repelling) areas and during driographic printing,only ink is supplied to the master.

Printing masters are generally obtained by the image-wise exposure andprocessing of an imaging material called a plate precursor. A typicalpositive-working plate precursor includes a hydrophilic support and anoleophilic coating which is not readily soluble in an aqueous alkalinedeveloper in the non-exposed state and becomes soluble in the developerafter exposure to radiation. In addition to the well knownphotosensitive imaging materials which are suitable for UV contactexposure through a film mask (the so-called pre-sensitized plates),heat-sensitive printing plate precursors have also become very popular.Such thermal materials offer the advantage of daylight stability and areespecially used in the so-called computer-to-plate method (CtP) whereinthe plate precursor is directly exposed, i.e., without the use of a filmmask. The material is exposed to heat or to infrared light and thegenerated heat triggers a (physico-)chemical process, such as ablation,polymerization, insolubilization by cross-linking of a polymer or byparticle coagulation of a thermoplastic polymer latex, andsolubilization by the destruction of intermolecular interactions or byincreasing the penetrability of a development barrier layer.

Although some of these thermal processes enable plate making without wetprocessing, the most popular thermal plates form an image by aheat-induced solubility difference in an alkaline developer betweenexposed and non-exposed areas of the coating. The coating typicallyincludes an oleophilic binder, e.g., a phenolic resin, of which the rateof dissolution in the developer is either reduced (negative working) orincreased (positive working) by the image-wise exposure. Duringprocessing, the solubility differential leads to the removal of thenon-image (non-printing) areas of the coating, thereby revealing thehydrophilic support, while the image (printing) areas of the coatingremain on the support.

Typically, for a positive-working thermal plate, a dissolution inhibitoris added to a phenolic resin as a binder whereby the rate of dissolutionof the coating is reduced. Upon heating, this reduced rate ofdissolution of the coating is increased on the exposed areas comparedwith the non-exposed areas, resulting in a sufficient difference insolubility of the coating after image-wise recording by heat orIR-radiation. Many different dissolution inhibitors are known anddisclosed in the literature, such as organic compounds having anaromatic group and a hydrogen bonding site or polymers or surfactantsincluding siloxane or fluoroalkyl units.

The known heat-sensitive printing plate precursors typically include ahydrophilic support and a coating which is alkali-soluble in exposedareas (positive working material) or in non-exposed areas (negativeworking material) and an IR-absorbing compound. Such a coating typicallyincludes an oleophilic polymer which may be a phenolic resin such asnovolac, resol or a polyvinylphenolic resin. The phenolic resin can bechemically modified whereby the phenolic monomeric unit is substitutedby a group such as described in WO 99/01795, EP 934 822, EP 1 072 432,U.S. Pat. No. 3,929,488, EP 2 102 443, EP 2 102 444, EP 2 102 445, andEP 2 102 446. The phenolic resin can also been mixed with other polymerssuch as an acidic polyvinyl acetal as described in WO 2004/020484 or acopolymer including sulfonamide groups as described in U.S. Pat. No.6,143,464. The use of other polymeric binders in lithographic printingplates are described in WO 2001/09682, EP 933 682, WO 99/63407, WO2002/53626, EP 1 433 594 and EP 1 439 058.

The positive-working thermal plate may further include, between theheat-sensitive recording layer and the support, an intermediate layerincluding an alkali soluble resin. This intermediate layer can improvethe chemical resistance of the plate against press chemicals. This layerinduces an improved removal of the coating on the exposed areas. Typicalexamples of positive-working thermal plate materials having such a twolayer structure are described in, e.g., EP 864420, EP 909657, EP-A1011970, EP-A 1263590, EP-A 1268660, EP-A 1072432, EP-A 1120246, EP-A1303399, EP-A 1311394, EP-A 1211065, EP-A 1368413, EP-A 1241003, EP-A1299238, EP-A 1262318, EP-A 1275498, EP-A 1291172, WO 2003/74287, WO2004/33206, EP-A 1433594 and EP-A 1439058. However, in the non-exposedareas of these plates, the resistance of the coating for the alkalinedeveloper is poor whereby the difference in the dissolution rate betweenthe exposed and non-exposed areas is insufficient, i.e., the non-exposedareas are partially affected by the developer before the exposed areasare completely dissolved in the developer. As a result, it is difficultto form highly sharp and clear images, particularly highlights, i.e.,fine images including a dot pattern or fine lines, are difficult to bereproduced.

In a high quality plate, it is advantageous that such highlights can bereproduced within a sufficient developing latitude, i.e., smallfluctuations in developing time do not substantially affect the imageformed on the plates and this developing latitude is obtained when thedifference in the dissolution rate is improved.

EP 1 182 512 discloses an alkaline developing solution including anamphoteric or cationic surfactant for development of an infraredradiation-presensitized plate.

EP 1 400 856 discloses a method for making a lithographic printing platewhereby the exposed precursor is developed with an alkaline developingsolution including a cationic surfactant or a compound having three ormore ethylene oxide-terminal groups in the molecule thereof.

EP 1 211 065 discloses a positive-working heat-sensitive printing plateprecursor wherein the recording layer includes an organic quaternaryammonium salt.

The printing plates of the prior art suffer from an insufficientdeveloping latitude.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a method for making a heat-sensitivelithographic printing plate whereby excellent printing properties areobtained and whereby the developing latitude or exposure latitude areimproved. A preferred embodiment of the present invention has thecharacteristic feature that the developing solution in the developingstep includes a compound having at least two onium groups. Thiscompound, hereinafter also referred to as a “blocking agent”, which iscapable of reducing the solubility of the alkaline soluble resin of thecoating of a positive-working heat-sensitive printing plate precursorwhereby the resistance of the coating in the non-exposed areas againstthe alkaline developer is increased, is present in the precursor and/orin an alkaline developing solution or replenishing solution. By use ofcompounds mentioned in the prior art documents EP 1 182 512, EP 1 400856 and EP 1 211 065 an insufficient developing latitude is obtained.Therefore, the inventors have discovered this new compound which iscapable of improving the resistance of the coating in the non-exposedareas against the alkaline developer and is capable of improving thedeveloping latitude or the exposure latitude.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with a preferred embodiment of the present invention,there is provided a method for making a lithographic printing plateincluding the steps of: (1) providing a heat-sensitive lithographicprinting plate precursor including on a support having a hydrophilicsurface or which is provided with a hydrophilic layer, a heat-sensitivecoating, (2) image-wise exposing the precursor with IR-radiation orheat, and (3) developing the image-wise exposed precursor with analkaline developing solution including a compound having at least twoonium groups.

In a preferred embodiment of the present invention, the compound havingat least two onium groups has a structure according to Formula I:

whereinQ is a divalent group Q² when e and f are 0, a trivalent group Q³ whenthe sum of e and f is 1, or a tetravalent group Q⁴ when e and f are both1;Z^(a) to Z^(d) independently are onium groups;L^(a) to L^(d) independently are divalent linking groups; anda, b, c, d, e and f independently are 0 or 1, preferably a, b, c and dare 1.

In another preferred embodiment of the present invention, the compoundhaving at least two onium groups has a structure according to FormulaII:

whereinZ^(a) and Z^(b) independently are onium groups;L^(a) is a divalent linking group, -Z^(x)-L^(x)- represents a repeatingunit wherein Z^(x) and L^(x) represent respectively a divalent oniumgroup and a divalent linking group for each x-value; andx is 0, 1 or an integer >1, more preferably x is an integer rangingbetween 1 and 50, most preferably between 1 and 10.

In a more preferred embodiment of the present invention, the compoundhaving at least two onium groups has a structure according to FormulaIII:

Z^(a)-L-Z^(b),  Formula III

whereinL is a divalent linking group; andZ^(a) and Z^(b) independently are onium groups.

The divalent linking groups L^(a) to L^(d), each L^(x) and L in thecompounds of Formula I, II and III are preferably selected from thegroup consisting of a linear, branched or cyclic alkylene group such asa methylene, ethylene, propylene, butylene group, c-hexylene or1-methyl-ethylene; an arylene group such as a phenylene, naphtalene oran heteroarylene group; an arylene-alkylene group such as benzylidenegroup; a bis-alkylene aromatic hydrocarbon group such as o-, p- orm-bis-methylene benzene group; an oxy-alkylene group such as methyleneoxide, ethylene oxide or propylene oxide group; an oxy-arylene oroxy-heteroarylene group such as phenylene oxide; or a combination of twoor more of these groups. Each of these alkylene or arylene groups can besubstituted. The linking group of a preferred embodiment of the presentinvention is composed of at least one of these groups. In a preferredembodiment, the linking group is composed of one or two of these groupswhich are repeated for at least two times, more preferably for a numberranging between 2 and 15, most preferably between 3 and 8. The linkinggroup of a preferred embodiment of the present invention can also becomposed of two, three or more sequences of these groups wherein eachsequence contains at least two or more of these groups.

Examples of a divalent linking group are —(CH₂)—, —(CH₂)—(CH₂)—,—(CH₂)—(CH—CH₃)—, —(CR^(a)R^(b))_(n)—, —C—C₆H₁₀—, —(C₆H₄)—,—(CH₂)—(C₆H₄)—, —(CH₂)—(C₆H₄)—(CH₂)—, —O—(CH₂)—, —O—(CH₂)—(CH₂)—,—O—(CH₂)—(CH—CH₃)—, —(C₆H₄)—(C₆H₄)—, —O—(C₆H₄)—,—(CH₂)—(CH₂)—[—O—(CH₂)—(CH₂)—]_(m)—,

wherein R^(a) and R^(b) are independently hydrogen or an optionallysubstituted alkyl or aryl group; n is an integer ranging between 2 and15, preferably between 3 and 10, m is an integer ranging between 2 and15, preferably between 3 and 10.

Q² is a divalent group, preferably selected from the group consisting ofthe divalent linking groups as defined above.

Q³ is a trivalent group, preferably selected from the group consistingof —CR′<, CR′(-(L′)_(p)—)(-(L″)_(q)-)(-(L′″)_(r)-), —(C₆H₃)<,C₆H₃(-(L′)_(p)-)(-(L″)_(q)-)(-L′″)_(r)-), [—S<]⁺, [—NR′<]⁺, or [—PR′<]⁺;

whereineach of > and < represents two binding sites;R′, R″ and R′″ are hydrogen or an optionally substituted alkyl, aryl oraralkyl group;L′, L″ and L′″ are a divalent linking group, preferably selected fromthe group consisting of the divalent linking groups as defined above;andp, q and r independently are 0 or 1.

Q⁴ is a tetravalent group, preferably selected from the list of thefollowing groups: >C<, C(-(L′)_(p)—)(-(L″)_(q)—)(-(L′″)_(r)-)(-(L″″)_(s)-), >(C₆H₂)<,C₆H₂(-(L′)_(p)-)(-(L″)_(q)-)(-(L′″)_(r)-)(-(L″″)_(s)-), [>N<]⁺, or[>P<]⁺;

whereineach of > and < represents two binding sites;L′, L″ and L′″ are a divalent linking group, preferably selected fromthe group consisting of the divalent linking groups as defined above;andp, q, r and s independently are 0 or 1, preferably 1.

The onium groups Z^(a) to Z^(d) and Z^(x) in the compounds of Formula I,II and III are positively charged groups and preferably selected fromthe group consisting of primary amine salts, secondary amine salts,tertiary amine salts, quaternary ammonium salts, phosphonium salts orsulphonium salts.

The onium groups Z^(a) to Z^(d) are more preferably selected from thegroups consisting of one of the following structures:

wherein* denotes the binding site of the onium group with one site of thedivalent linking group;X represents oxygen, sulfur or —NR²—;each of R¹ to R⁵ groups are independently hydrogen; an optionallysubstituted alkyl, alkylene, aryl or aralkyl group such as methyl,ethyl, propyl, butyl, propenyl, butenyl, phenyl or benzyl; a halogenatom such as bromide or chloride; —CN; —NO₂; an oxy-alkyl or oxy-arylgroup; a thio-alkyl or thio-aryl group; an amide or sulphonamide group;a carboxylic acid or salt or alkyl ester group; a sulphonic acid or saltor alkyl ester group; a sulphonalkyl or sulphonaryl group; an aminogroup; or whereby two groups of the R¹ to R⁵ groups together include thenecessary atoms to form a cyclic structure, preferably a 5- or6-membered ring;each of R⁶ to R⁸ groups are independently hydrogen; an optionallysubstituted alkyl, alkylene, aryl or aralkyl group such as methyl,ethyl, propyl, butyl, propenyl, butenyl, phenyl or benzyl; a carboxylicacid or salt or alkyl ester group; or whereby two groups of the R⁶ to R⁸groups together include the necessary atoms to form a cyclic structure,preferably a 5- or 6-membered ring.

Each of the onium groups Z^(x) in the compounds of Formula II arepositively charged groups having two binding sites, i.e., divalent, andmore preferably selected from the list of the onium groups as abovewherein one of the R¹ to R⁸ groups is not present and is replaced by *,indicating the second binding site.

In order to obtain electrical neutrality, one or more anions are presentas a counterion. Examples of such counterions are chloride, bromide,iodide, or a compound including at least one of the following anionicgroups: a sulphonate, sulphate, carboxylate, phosphate or phosphonateanion, or wherein the sulphonate, sulphate, carboxylate, phosphate orphosphonate anion is part of one of the substituting groups R¹ to R⁵ ofthe onium group as defined above. Preferred counterions are bromide,chloride, methyl sulphonate or tosylate.

The onium groups Z^(a) to Z^(d) in the compounds of Formula I preferablyhave the same structure.

The onium groups Z^(a) and Z^(b) in the compounds of Formula IIpreferably have the same structure.

All the Z^(x) groups in the compounds of Formula II preferably have thesame structure.

The onium groups Z^(a) and Z^(b) in the compounds of Formula IIIpreferably have the same structure.

Examples of blocking agents of preferred embodiments of the presentinvention are:

During developing of an image-wise exposed heat-sensitive lithographicprinting plate precursor, the blocking agent of a preferred embodimentof the present invention is present in the aqueous alkaline developingsolution.

In accordance with a preferred embodiment of the present invention, theblocking agent is present in the alkaline developing solution at thestart of the developing process.

In accordance with another preferred embodiment of the presentinvention, the blocking agent is added to the alkaline developingsolution during the developing process, preferably as a solution ordispersion. In a more preferred embodiment, the blocking agent is addedto the alkaline developing solution by the addition of a replenishingsolution including the blocking agent during the developing process.

In accordance with another preferred embodiment of the presentinvention, the blocking agent is added to the alkaline developingsolution during the developing process by removing at least a portion ofthe precursor including the blocking agent. The blocking agent can bepresent in the heat-sensitive coating, an intermediate layer between thesupport and the heat-sensitive coating, a top layer and/or a layer onthe back side of the plate.

Developing Solution

The aqueous alkaline developing solution (hereinafter also referred toas “developer”) may include an alkaline agent. The composition of theaqueous alkaline solution can be selected from conventional alkalinedevelopers.

The aqueous alkaline developing solution of a preferred embodiment ofthe present invention preferably has a pH value of at least 10, morepreferably of at least 11.5, most preferably of at least 12. There is nospecific upper limit for the pH but the pH is usually not higher than14.

The alkaline agent preferably includes inorganic alkaline agents such assodium hydroxide, potassium hydroxide, lithium hydroxide, sodiumtertiary phosphate, potassium tertiary phosphate, ammonium tertiaryphosphate, sodium secondary phosphate, potassium secondary phosphate,ammonium secondary phosphate, sodium carbonate, potassium carbonate,ammonium carbonate, sodium bicarbonate, potassium bicarbonate, ammoniumbicarbonate, sodium borate, potassium borate and ammonium borate, andpotassium citrate, sodium citrate and the like.

The alkaline agent may also include organic alkaline agents such asmonomethylamine, dimethylamine, trimethylamine, monoethylamine,diethylamine, triethylamine, monoisopropylamine, diisopropylamine,triisopropylamine, n-butylamine, monoethanolamine, diethanolamine,triethanolamine, monoisopropanolamine, diisopropanolamine,ethylenediamine, pyridine and the like.

The alkaline aqueous solution may also include an alkaline silicate. Thealkaline silicate may be those exhibiting an alkalinity when dissolvedin water, and examples thereof include an alkali metal silicate andalkali metal metasilicate such as sodium silicate, sodium metasilicate,potassium silicate and lithium silicate, and ammonium silicate. Thealkaline silicate may be used alone, or in combination.

The development performance of the alkaline aqueous solution may beeasily modulated by adjusting a molar ratio of alkaline silicates andalkali metal hydroxides, represented by silicon oxide (SiO₂) and analkali oxide (M₂O, wherein M represents an alkali metal or an ammoniumgroup). The alkaline aqueous solution preferably has a molar ratioSiO₂/M₂O from 0.5 to 3.0, and more preferably from 1.0 to 2.0. When themolar ratio SiO₂/M₂O is less than 0.5, alkalinity of the solutionstrengthens so as to cause a harmful effect such as etching of analuminum plate which is generally used as a substrate in a lithographicprinting plate precursor. When the molar ratio, SiO₂/M₂O is more than3.0, the development performance of the solution may be degraded.

The concentration of alkaline silicate in the developer ranges generallyfrom 1 to 14% by weight, preferably from 3 to 14% by weight, and morepreferably from 4 to 14% by weight. When the concentration is less than1% by weight, the development performance or treatment capacity may bedegraded. When the concentration is more than 14% by weight,precipitated materials or crystals may be easily generated, and gelationmay be easily caused during neutralization of waste liquid, resulting inan obstacle to the waste disposal.

The developer based on an alkaline aqueous solution may also include anonreducing sugar. The nonreducing sugar denotes sugars having noreductive property due to the absence of a free aldehyde group or a freeketone group. The nonreducing sugar is classified into trehalose-typeoligosaccharides wherein a reductive group and another reductive groupmake a linkage; glycosides wherein a reductive group in a sugar islinked to a non-sugar compound; and sugar alcohols which are produced byreducing a sugar by hydrogenation. The trehalose-type oligosaccharidesinclude sucrose and trehalose, and the glycosides include alkylglycosides, phenol glycosides, mustard oil glycosides and the like. Thesugar alcohols include D,L-arabitol, ribitol, xylitol, D,L-sorbitol,D,L-mannitol, D,L-iditol, talitol, dulcitol, allodulcitol and the like.Further, maltitol obtained by hydrogenation of disaccharide, a reducedmaterial obtained by hydrogenation of oligosaccharide (a reduced starchsyrup) and the like are preferably used. In the above nonreducing sugar,preferred are sugar alcohols and sucrose, and particularly preferred areD-sorbitol, sucrose and a reduced starch syrup, since they havebuffering action in appropriate pH range.

The above nonreducing sugar may be used alone or in combination withother ingredients, and the concentration thereof in the developer rangesgenerally from 0.1 to 30% by weight, and preferably from 1 to 20% byweight.

In the developer, an alkaline agent may be used as a base in combinationwith the above mentioned alkaline silicate or nonreducing sugar, and thealkaline agent may be selected from sodium hydroxide and potassiumhydroxide. Further, sodium tertiary phosphate, potassium tertiaryphosphate, sodium carbonate and potassium carbonate are also preferable,since they have themselves a buffering action. The above alkaline agentmay be used alone or in combination.

The developer may optionally contain further components, such as buffersubstances, complexing agents, antifoaming agents, organic solvents,antisludge agent, corrosion inhibitors, dyes, surfactants and/orhydrotropic agents as known in the art.

In the aqueous alkaline developing solution, it is possible tosimultaneously use organic solvents having solubility in water at 20° C.of not more than 15% by weight according to need. Examples of suchorganic solvents are such carboxilic acid esters as ethyl acetate,propyl acetate, butyl acetate, amyl acetate, benzyl acetate, ethyleneglycol monobutyl ether acetate, butyl lactate and butyl levulinate; suchketones as ethyl butyl ketone, methyl isobutyl ketone and cyclohexanone;such alcohols as ethylene glycol monobutyl ether, ethylene glycol benzylether, ethylene glycol monophenyl ether, benzyl alcohol,methylphenylcarbitol, n-amyl alcohol and methylamyl alcohol; suchalkyl-substituted aromatic hydrocarbons as xylene; and such halogenatedhydrocarbons as methylene dichloride and monochlorobenzene. Theseorganic solvents may be used alone or in combination. Particularlypreferred is benzyl alcohol. These organic solvents are added to thedeveloper or replenisher therefor generally in an amount of not morethan 10% by weight and preferably not more than 5% by weight.

Besides the components described above, the developing solution of apreferred embodiment of the present invention includes a non-ionicsurfactant. Such a non-ionic surfactant may be used as a dissolutionpreventing agent whereby undercutting of non-exposed areas is reduced.Examples of nonionic surfactants include ethoxylated alcohols,polyethylene glycols and polyhydric alcohols. Ethoxylated alcohols arepreferred, and in particular, ethoxylated alcohols having ahydrophilic-lipophilic balance (HLB) higher than 5 are more preferred.Specific examples of nonionic surfactants are listed below: polyethyleneglycol, polyoxyethylene lauryl ether, laurylalcohol polyglycol ethers,oleyl alcohol ethoxylated, lanolin alcohol ethoxylated, dodecanolethoxylated, cetostearyl alcohol ethoxylated, tetramethyldecindiolethoxylated, polyoxyethylene nonyl ether, polyoxyethylene cetyl ether,polyoxyethylene stearyl ether, polyoxyethylene oleyl ether,polyoxyethylene behenyl ether, polyoxyethylene polyoxypropylene blockcopolymers, polyoxyethylene polyoxypropylene cetyl ether,polyoxyethylene polyoxypropylene behenyl ether, polyoxyethylenenonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylenestearylamine, polyoxyethylene oleylamine, polyoxyethylene stearic acidamide, polyoxyethylene oleic acid amide, polyoxyethylene castor oil,polyoxyethylene abietyl ether, polyoxyethylene lanolin ether,polyoxyethylene monolaurate, polyoxyethylene monostearate,polyoxyethylene glyceryl monooleate, polyoxyethylene glycerylmonostearate, polyoxyethylene propylene glycol monostearate,polyoxyethylene sorbitan monolaurate, and sorbitan monolaurate. Thenon-ionic surfactants, which have an ethylene diamine group, substitutedwith groups of polyoxyethylene, polyoxypropylene or mixtures thereof,are of special interest in the developing solution. Examples of suchnon-ionic surfactants are the TETRONIC surfactants commerciallyavailable from BASF.

The non-ionic surfactants preferably have an average molecular weightranging from 500 to 10,000, preferably from 1,000 to 5,000. They can beincluded individually or as admixture of two or more compounds in anamount ranging from 0.05 to 5%, preferably from 0.1 to 1% by weight ofthe total developing solution.

The developers used in a preferred embodiment of the present inventionmay simultaneously contain another surfactant for the purpose ofimproving developing properties thereof. By incorporating surfactants tothe developer solution, the surface tension reduces drastically and thedeveloper solution becomes effective, i.e., removal of the non-imageareas without occurrence of stain/toning, at a lower pH compared to thesame developer solution without a surfactant. The developer may includean ionic surfactant such as an anionic or cationic surfactant, anon-ionic surfactant and/or amphoteric surfactants such as LibratericAA30 (trademark from Libra Chemicals Limited). Examples of suchsurfactants include salts of higher alcohol (C8˜C22) sulfuric acidesters such as sodium salt of lauryl alcohol sulfate, sodium salt ofoctyl alcohol sulfate, ammonium salt of lauryl alcohol sulfate, TeepolB-81 (trade mark, available from Shell Chemicals Co., Ltd.) and sodiumalkyl sulfates; salts of aliphatic alcohol phosphoric acid esters suchas sodium salt of cetyl alcohol phosphate; alkyl aryl sulfonic acidsalts such as sodium salt of dodecylbenzene sulfonate, sodium salt ofisopropylnaphthalene sulfonate, sodium salt of dinaphthalene disulfonateand sodium salt of metanitrobenzene sulfonate; sulfonic acid salts ofalkylamides such as C₁₇H₃₃CON(CH₃)CH₂CH₂SO₃Na and sulfonic acid salts ofdibasic aliphatic acid esters such as sodium dioctyl sulfosuccinate andsodium dihexyl sulfosuccinate. These surfactants may be used alone or incombination. Particularly preferred are sulfonic acid salts. Thesesurfactants may be used in an amount of generally not more than 5% byweight and preferably not more than 3% by weight.

The cationic surfactant used in the developer may include amine salts,quaternary ammonium salts, phosphonium salts, sulfonium salts and thelike. Examples of the amine salts are primary amine salts, secondaryamine salts, tertiary amine salts, and imidazoline salts. Examples ofthe quaternary ammonium salts include tetraalkyl quaternary ammoniumsalts, trialkyl benzyl quaternary ammonium salts, alkyl pyridiniumsalts, alkyl quinolinium salts, imidazolinium salts andbenzimidazolinium salts.

Exemplary amphoteric surfactants include betaine derivatives, such as,for example, alkylamidopropyl betaine, alkyldimethyl betaine,bishydroxyethyl betaine, alkylamido propyl betaine, lauryl betaine, andthe like, glycine derivatives, such as, for example, cocoamphocarboxyglycinate, lauroamphocarboxy glycinate, caprylamphocarboxy glycinate,oleoamphocarboxy glycinate, oleoamphopolycarboxy glycinate, N-alkylglycinate, and the like, imino derivatives, such as, for example,cocoiminodipropionate, octyliminodipropionate, and the like, imidazolinederivatives, such as, for example, coconut imidazoline, and the like,lecithin derivatives, and aminocarboxylic acids. These amphotericsurfactants preferably have an average molecular weight ranging from 100to 10,000, preferably from 1,000 to 5,000. They can be includedindividually or as an admixture of two or more compounds.

The above described anionic and amphoteric surfactant can be present inthe developing solution in a total amount ranging from 0.5 to 10%,preferably from 1 to 6%, and more preferably from 1 to 3% by weight ofthe total developing solution.

In order to enhance developing stability of the developers, thefollowing compounds may simultaneously be used. Examples of suchcompounds are neutral salts such as NaCl, KCl and KBr as disclosed inJP-A-58-75152; chelating agents such as EDTA and NTA as disclosed inJP-A-58-190 952 (U.S. Pat. No. 4,469,776), complexes such as[Co(NH₃)₆]Cl₃ as disclosed in JP-A-59-121336 (U.S. Pat. No. 4,606,995);ionizable compounds of elements of the group IIa, IIIa or IIIb of thePeriodic Table such as those disclosed in JP-A-55-25100; anionic oramphoteric surfactants such as sodium alkyl naphthalene sulfonate andN-tetradecyl-N,N-dihydroxyethyl betaine as disclosed in JP-A-50-51324;tetramethyldecyne diol as disclosed in U.S. Pat. No. 4,374,920;non-ionic surfactants as disclosed in JP-A-60-213943; cationic polymerssuch as methyl chloride quaternary products of p-dimethylaminomethylpolystyrene as disclosed in JP-A-55-95946; amphoteric polyelectrolytessuch as copolymer of vinylbenzyl trimethylammonium chloride and sodiumacrylate as disclosed in JP-A-56-142528; reducing inorganic salts suchas sodium sulfite as disclosed in JP-A-57-192952 (U.S. Pat. No.4,467,027) and alkaline-soluble mercapto compounds or thioethercompounds such as thiosalicylic acid, cysteine and thioglycolic acid;inorganic lithium compounds such as lithium chloride as disclosed inJP-A-58-59444; organic lithium compounds such as lithium benzoate asdisclosed in JP-A-50-34442; organometallic surfactants containing Si, Tior the like as disclosed in JP-A-59-75255; organoboron compounds asdisclosed in JP-A-59-84241 (U.S. Pat. No. 4,500,625); quaternaryammonium salts such as tetraalkylammonium oxides as disclosed inEP-A-101 010; and bactericides such as sodium dehydroacetate asdisclosed in JP-A-63-226657.

In a preferred embodiment of the present invention, the blocking agentis present in a developing solution at a concentration of at least 0.01g/l, preferably in a concentration ranging between 0.05 and 30 g/l, morepreferably between 0.05 and 15 g/l, more preferably between 0.05 and 5g/l, most preferably between 0.1 and 1 g/l.

Replenishing Solution

During the development, the non-image areas of the coating are removedwith an aqueous alkaline developer solution optionally in combinationcombined with mechanical rubbing, e.g., by a rotating brush. During thedevelopment step, any water-soluble layer present is preferably alsoremoved. The development is preferably carried out at temperatures offrom 20 to 40° C. in automated processing units as customary in the art.

To perform development processing stably for a long time period, it isparticularly important to control the strength of alkali and theconcentration of silicates and other ingredients in the developer.Therefore, a replenishing solution, hereinafter also referred to asreplenisher, is added to the developing solution, usually in smallamounts such that a stable development processing can be performed overa long time period without exchanging the developer. Therefore, it isalso important that the concentration of the blocking agent is presentin the developing solution at a sufficiently high level in order tomaintain the developing latitude or exposure latitude of the precursorand this can be realized by adding a replenishing solution including theblocking agent of a preferred embodiment of the present invention.

For regeneration, the replenishing solution, hereinafter also referredto as replenisher, preferably includes active ingredients of thedeveloping solution such as alkaline agent. The replenishing solution isadded continuously or in small amounts to the developing solution duringor after the developing process in order to regulate the concentrationof the active ingredients in the developing solution at a levelsufficiently high or at a constant level such that the development ofimage-wise exposed precursors remains at a constant level. The requiredamounts of regenerated material must be tailored to the developingapparatuses used, daily plate throughputs, image areas, etc., and are ingeneral from 1 to 150 ml per square meter of plate precursor. Theaddition of replenisher can be regulated, for example, by measuring theconductivity of the developer as described in EP-A 0 556 690.

In the method for development processing, any known process ofsupplementing a replenisher for developer may also be employed. Examplesof such methods preferably used are a method for intermittently orcontinuously supplementing a replenisher as a function of the amount ofplates processed and time as disclosed in JP-A-55-115039 (GB-A-2 046931), a method including disposing a sensor for detecting the degree oflight-sensitive layer dissolved out in the middle portion of adeveloping zone and supplementing the replenisher in proportion to thedetected degree of the light-sensitive layer dissolved out as disclosedin JP-A-58-95349 (U.S. Pat. No. 4,537,496); a method includingdetermining the impedance value of a developer and processing thedetected impedance value by a computer to perform supplementation of areplenisher as disclosed in GB-A-2 208 249.

In a preferred embodiment of the present invention, the blocking agentis present in a replenishing solution at a concentration of at least0.05 g/l, preferably in a concentration ranging between 0.1 and 30 g/l,more preferably between 0.5 and 20 g/l, more preferably between 0.5 and15 g/l, most preferably between 0.5 and 10 g/l. In another preferredembodiment, the ratio of the concentration of the blocking agent in thereplenishing solution, containing at least 0.05 g/l of the blockingagent, and in the developing solution is preferably between 0.5 and 100,more preferably between 1.1 and 100, most preferably between 2 and 50.

The replenishing solution preferably has a pH value of at least 10, morepreferably of at least 11.5, most preferably of at least 12. There is nospecific upper limit for the pH but the pH is usually not higher than14.

In another preferred embodiment of the present invention, more than onereplenishing solution can be used for adding to the developing solutionduring or after the development processing and these replenishers maycontain different types in different amounts of blocking agents, andalso different types in different amounts of other compounds forimproving the development processing.

In a more preferred embodiment of the present invention, the freshdeveloping solution at starting the development processing for the firsttime is essentially free of the blocking agent according to a preferredembodiment of the present invention and during or after processingprecursors, a replenishing solution, containing the blocking agent, isadded to the developing solution and/or a layer of the precursor,including the blocking agent, is removed at least partially in thedeveloping solution.

The heat-sensitive lithographic printing plate precursor of a preferredembodiment of the present invention includes a support having ahydrophilic surface or which is provided with a hydrophilic layer, and,on the support, a heat-sensitive coating.

Support

The support of the lithographic printing plate precursor has ahydrophilic surface or is provided with a hydrophilic layer. The supportmay be a sheet-like material such as a plate or it may be a cylindricalelement such as a sleeve which can be slid around a print cylinder of aprinting press. A preferred support is a metal support such as aluminumor stainless steel. The metal can also be laminated to a plastic layer,e.g., polyester film.

A particularly preferred lithographic support is an electrochemicallygrained and anodized aluminum support.

Graining and anodization of aluminum is well known in the art. Theanodized aluminum support may be treated to improve the hydrophilicproperties of its surface. For example, the aluminum support may besilicated by treating its surface with a sodium silicate solution atelevated temperature, e.g., 95° C. Alternatively, a phosphate treatmentmay be applied which involves treating the aluminum oxide surface with aphosphate solution that may further contain an inorganic fluoride.Further, the aluminum oxide surface may be rinsed with a citric acid orcitrate solution. This treatment may be carried out at room temperatureor may be carried out at a slightly elevated temperature of about 30 to50° C. A further interesting treatment involves rinsing the aluminumoxide surface with a bicarbonate solution. Still further, the aluminumoxide surface may be treated with polyvinylphosphonic acid,polyvinylmethylphosphonic acid, phosphoric acid esters of polyvinylalcohol, polyvinylsulfonic acid, polyvinylbenzenesulfonic acid, sulfuricacid esters of polyvinyl alcohol, and acetals of polyvinyl alcoholsformed by reaction with a sulfonated aliphatic aldehyde. It is furtherevident that one or more of these post treatments may be carried outalone or in combination. More detailed descriptions of these treatmentsare given in GB-A 1 084 070, DE-A 4 423 140, DE-A 4 417 907, EP-A 659909, EP-A 537 633, DE-A 4 001 466, EP-A 292 801, EP-A 291 760 and U.S.Pat. No. 4,458,005.

Coating

The heat-sensitive coating, which is provided on the support, may bepositive-working or negative-working. A positive-working heat-sensitivecoating is preferred. The coating of a positive-working heat-sensitivecoating does not dissolve in an alkaline developing solution in theunexposed areas and becomes soluble in the exposed areas within the timeused for developing the plate. The coating preferably includes aninfrared absorbing agent and an alkaline soluble oleophilic resinwherein the solubility in an alkaline developing solution is reduced inthe coating and wherein the solubility in an alkaline developingsolution is increased upon heating or IR-radiation. The coatingpreferably further includes a dissolution inhibitor whereby the rate ofdissolution in an alkaline developing solution is reduced. Due to thissolubility differential the rate of dissolution of the exposed areas issufficiently higher than in the non-exposed areas.

In a preferred embodiment of the present invention, the heat-sensitivecoating includes a first polymer which is a phenolic resin such asnovolac, resol or a polyvinylphenolic resin; novolac is more preferred.Typical examples of such polymers are described in DE-A-4007428,DE-A-4027301 and DE-A-4445820. Other preferred polymers are phenolicresins wherein the phenyl group or the hydroxy group of the phenolicmonomeric unit are chemically modified with an organic substituent asdescribed in EP 894 622, EP 901 902, EP 933 682, WO 99/63407, EP 934822, EP 1 072 432, U.S. Pat. No. 5,641,608, EP 982 123, WO 99/01795, WO04/035310, WO 04/035686, WO 04/035645, WO 04/035687 or EP 1 506 858.

The novolac resin or resol resin may be prepared by polycondensation ofat least one member selected from aromatic hydrocarbons such as phenol,o-cresol, p-cresol, m-cresol, 2,5-xylenol, 3,5-xylenol, resorcinol,pyrogallol, bisphenol, bisphenol A, trisphenol, o-ethylphenol,p-etylphenol, propylphenol, n-butylphenol, t-butylphenol, octyl-phenol,1-naphtol and 2-naphtol, with at least one aldehyde or ketone selectedfrom aldehydes such as formaldehyde, glyoxal, acetoaldehyde,propionaldehyde, benzaldehyde and furfural and ketones such as acetone,methyl ethyl ketone and methyl isobutyl ketone, in the presence of anacid catalyst. Instead of formaldehyde and acetaldehyde,paraformaldehyde and paraldehyde may, respectively, be used.

The weight average molecular weight, measured by gel permeationchromatography using universal calibration and polystyrene standards, ofthe novolac resin is preferably from 500 to 150,000 g/mol, morepreferably from 1,500 to 50,000 g/mol.

The poly(vinylphenol) resin may also be a polymer of one or morehydroxy-phenyl containing monomers such as hydroxystyrenes orhydroxy-phenyl(meth)acrylates. Examples of such hydroxystyrenes areo-hydroxystyrene, m-hydroxystyrene, p-hydroxystyrene,2-(o-hydroxyphenyl)propylene, 2-(m-hydroxyphenyl)propylene and2-(p-hydroxyphenyl)propylene. Such a hydroxystyrene may have asubstituent such as chlorine, bromine, iodine, fluorine or a C₁₋₄ alkylgroup, on its aromatic ring. An example of suchhydroxy-phenyl(meth)acrylate is 2-hydroxy-phenyl methacrylate.

The poly(vinylphenol) resin may usually be prepared by polymerizing oneor more hydroxy-phenyl containing monomer in the presence of a radicalinitiator or a cationic polymerization initiator. The poly(vinylphenol)resin may also be prepared by copolymerizing one or more of thesehydroxy-phenyl containing monomers with other monomeric compounds suchas acrylate monomers, methacrylate monomers, acrylamide monomers,methacrylamide monomers, vinyl monomers, aromatic vinyl monomers ordiene monomers.

The weight average molecular weight, measured by gel permeationchromatography using universal calibration and polystyrene standards, ofthe poly(vinylphenol) resin is preferably from 1,000 to 200,000 g/mol,more preferably from 1,500 to 50,000 g/mol.

Examples of phenolic resins are:

-   POL-01: ALNOVOL SPN452 is a solution of a novolac resin, 40% by    weight in Dowanol PM, obtained from CLARIANT GmbH.-   Dowanol PM consists of 1-methoxy-2-propanol (>99.5%) and    2-methoxy-1-propanol (<0.5%).-   POL-02: ALNOVOL SPN400 is a solution of a novolac resin, 44% by    weight in Dowanol PMA, obtained from CLARIANT GmbH.    Dowanol PMA consists of 2-methoxy-1-methyl-ethylacetate.-   POL-03: ALNOVOL HPN100 a novolac resin obtained from CLARIANT GmbH.-   POL-04: DURITE PD443 is a novolac resin obtained from BORDEN CHEM.    INC.-   POL-05: DURITE SD423A is a novolac resin obtained from BORDEN CHEM.    INC.-   POL-06: DURITE SD126A is a novolac resin obtained from BORDEN CHEM.    INC.-   POL-07: BAKELITE 6866LB02 is a novolac resin obtained from BAKELITE    AG.-   POL-08: BAKELITE 6866LB03 is a novolac resin obtained from BAKELITE    AG.-   POL-09: KR 400/8 is a novolac resin obtained from KOYO CHEMICALS    INC.-   POL-10: HRJ 1085 is a novolac resin obtained from SCHNECTADY    INTERNATIONAL INC.-   POL-11: HRJ 2606 is a phenol novolac resin obtained from SCHNECTADY    INTERNATIONAL INC.-   POL-12: LYNCUR CMM is a copolymer of 4-hydroxy-styrene and methyl    methacrylate obtained from SIBER HEGNER.

In another preferred embodiment of the present invention, theheat-sensitive coating further includes a second polymer which isinsoluble in water and soluble in an alkaline solution.

In accordance with a more preferred embodiment of the present invention,the heat-sensitive coating includes a heat-sensitive layer and anintermediate layer. The intermediate layer is present between theheat-sensitive layer and the hydrophilic surface of the support. In astill more preferred embodiment, the heat-sensitive layer includes afirst polymer and optionally an inhibitor, and the intermediate layerincludes a second polymer.

The second polymer is preferably an organic polymer which has acidicgroups with a pKa of less than 13 to ensure that the layer is soluble orat least swellable in aqueous alkaline developers. Advantageously, thebinder is a polymer or polycondensate, for example, a polyester, apolyamide resin, an epoxy resin, an acetal resin, an acrylic resin, amethacrylic resin, a styrene based resin, a polyurethane resin orpolyurea.

More preferably, the second polymer has one or more functional groupsselected from the list of:

-   -   (i) a sulfonamide group such as —SO₂—NH—R^(g) wherein R^(g)        represents a hydrogen or an optionally substituted hydrocarbon        group such as an optionally substituted alkyl, aryl or        heteroaryl group;    -   (ii) an active imide group such as —SO₂—NH—CO—R^(h),        —SO₂—NH—SO₂—R^(h) or —CO—NH—SO₂—R^(h) wherein R^(h) represents a        hydrogen or an optionally substituted hydrocarbon group such as        an optionally substituted alkyl, aryl or heteroaryl group;    -   (iii) a carboxylate group;    -   (iv) a sulfonate group;    -   (v) phosphonate group, and    -   (vi) a phosphate group;        a sulfonamide group or an active imide group are more preferred;        most preferred are polymers selected from a copolymer including        a N-benzyl-maleimide monomeric unit or a monomeric unit        including a sulfonamide group as described in EP-A 933 682, EP 0        894 622 (page 3, line 16 to page 6, line 30), EP-A 0 982 123        (page 3, line 56 to page 51, line 5), EP-A 1 072 432 (page 4,        line 21 to page 10, line 29) and WO 99/63407 (page 4, line 13 to        page 9, line 37).

Other polymers having an acidic group are polycondensates and polymershaving free phenolic hydroxyl groups, as obtained, for example, byreacting phenol, resorcinol, a cresol, a xylenol or a trimethylphenolwith aldehydes, especially formaldehyde, or ketones. Condensates ofsulfamoyl- or carbamoyl-substituted aromatics and aldehydes or ketonesare also suitable. Polymers of bismethylol-substituted ureas, vinylethers, vinyl alcohols, vinyl acetals or vinylamides and polymers ofphenylacrylates and copolymers of hydroxy-phenylmaleimides are likewisesuitable. Furthermore, polymers having units of vinylaromatics,N-aryl(meth)acrylamides or aryl(meth)acrylates may be mentioned, itbeing possible for each of these units also to have one or more carboxylgroups, phenolic hydroxyl groups, sulfamoyl groups or carbamoyl groups.Specific examples include polymers having units of2-hydroxyphenyl(meth)acrylate, of N-(4-hydroxyphenyl)(meth)acrylamide,of N-(4-sulfamoylphenyl)-(meth)acrylamide, ofN-(4-hydroxy-3,5-dimethylbenzyl)-(meth)acrylamide, or 4-hydroxystyreneor of hydroxyphenylmaleimide. The polymers may additionally containunits of other monomers which have no acidic units. Such units includevinylaromatics, methyl(meth)acrylate, phenyl(meth)acrylate,benzyl(meth)acrylate, methacrylamide or acrylonitrile.

Dissolution Inhibitor

In a preferred embodiment of the present invention, the heat-sensitivecoating or the heat-sensitive layer also contain one or more dissolutioninhibitors. Dissolution inhibitors are compounds which reduce thedissolution rate of the hydrophobic polymer in the aqueous alkalinedeveloper at the non-exposed areas of the coating and wherein thisreduction of the dissolution rate is destroyed by the heat generatedduring the exposure so that the coating readily dissolves in thedeveloper at exposed areas. The dissolution inhibitor exhibits asubstantial latitude in the dissolution rate between the exposed andnon-exposed areas. By preference, the dissolution inhibitor has a gooddissolution rate latitude when the exposed coating areas have dissolvedcompletely in the developer before the non-exposed areas are attacked bythe developer to such an extent that the ink-accepting capability of thecoating is affected. The dissolution inhibitor(s) can be added to thelayer which includes the hydrophobic polymer discussed above.

The dissolution rate of the non-exposed coating in the developer ispreferably reduced by interaction between the hydrophobic polymer andthe inhibitor, due to, e.g., hydrogen bonding between these compounds.Suitable dissolution inhibitors are preferably organic compounds whichinclude at least one aromatic group and a hydrogen bonding site, e.g., acarbonyl group, a sulfonyl group, or a nitrogen atom which may bequaternized and which may be part of a heterocyclic ring or which may bepart of an amino substituent of the organic compound. Suitabledissolution inhibitors of this type have been disclosed in, e.g., EP-A825 927 and 823 327.

Water-repellent polymers represent another type of suitable dissolutioninhibitors. Such polymers seem to increase the developer resistance ofthe coating by repelling the aqueous developer from the coating. Thewater-repellent polymers can be added to the layer including the firstpolymer and/or can be present in a separate layer provided on top of thelayer with the first polymer. In the latter preferred embodiment, thewater-repellent polymer forms a barrier layer which shields the coatingfrom the developer and the solubility of the barrier layer in thedeveloper or the penetrability of the barrier layer by the developer canbe increased by exposure to heat or infrared light, as described in,e.g., EP-A 864420, EP-A 950 517 and WO 99/21725. Preferred examples ofthe water-repellent polymers are polymers including siloxane and/orperfluoroalkyl units. In a preferred embodiment, the coating containssuch a water-repellent polymer in an amount between 0.5 and 25 mg/m²,preferably between 0.5 and 15 mg/m² and most preferably between 0.5 and10 mg/m². When the water-repellent polymer is also ink-repelling, e.g.,in the case of polysiloxanes, higher amounts than 25 mg/m² can result inpoor ink-acceptance of the non-exposed areas. An amount lower than 0.5mg/m₂ on the other hand may lead to an unsatisfactory developmentresistance. The polysiloxane may be a linear, cyclic or complexcross-linked polymer or copolymer. The term polysiloxane compound shallinclude any compound which contains more than one siloxane group—Si(R,R′)—O—, wherein R and R′ are optionally substituted alkyl or arylgroups. Preferred siloxanes are phenylalkylsiloxanes anddialkylsiloxanes. The number of siloxane groups in the (co)polymer is atleast 2, preferably at least 10, more preferably at least 20. It may beless than 100, preferably less than 60. In another preferred embodiment,the water-repellent polymer is a block-copolymer or a graft-copolymer ofa poly(alkylene oxide) block and a block of a polymer including siloxaneand/or perfluoroalkyl units. A suitable copolymer includes about 15 to25 siloxane units and 50 to 70 alkylene oxide groups. Preferred examplesinclude copolymers including phenylmethylsiloxane and/ordimethylsiloxane as well as ethylene oxide and/or propylene oxide, suchas Tego Glide 410, Tego Wet 265, Tego Protect 5001 or Silikophen P50/X,all commercially available from Tego Chemie, Essen, Germany. Such acopolymer acts as a surfactant which upon coating, due to itsbifunctional structure, automatically positions itself at the interfacebetween the coating and air and thereby forms a separate top layer evenwhen the whole coating is applied from a single coating solution.Simultaneously, such surfactants act as a spreading agent which improvesthe coating quality. Alternatively, the water-repellent polymer can beapplied in a second solution, coated on top of the layer including thehydrophobic polymer. In that preferred embodiment, it may beadvantageous to use a solvent in the second coating solution that is notcapable of dissolving the ingredients present in the first layer so thata highly concentrated water-repellent phase is obtained at the top ofthe coating.

Development Accelerator

Preferably, also one or more development accelerators are included inthe heat-sensitive coating or in the heat-sensitive layer, i.e.,compounds which act as dissolution promoters because they are capable ofincreasing the dissolution rate of the non-exposed coating in thedeveloper. The simultaneous application of dissolution inhibitors andaccelerators allows a precise fine tuning of the dissolution behavior ofthe coating. Suitable dissolution accelerators are cyclic acidanhydrides, phenols or organic acids. Examples of the cyclic acidanhydride include phthalic anhydride, tetrahydrophthalic anhydride,hexahydrophthalic anhydride, tetrachlorophthalic anhydride, maleicanhydride, chloromaleic anhydride, alpha-phenylmaleic anhydride,succinic anhydride, and pyromellitic anhydride, as described in U.S.Pat. No. 4,115,128. Examples of the phenols include bisphenol A,p-nitrophenol, p-ethoxyphenol, 2,4,4′-trihydroxybenzophenone,2,3,4-trihydroxy-benzophenone, 4-hydroxybenzophenone,4,4′,4″-trihydroxy-triphenylmethane, and4,4′,3″,4″-tetrahydroxy-3,5,3′,5′-tetramethyltriphenyl-methane, and thelike. Examples of the organic acids include sulfonic acids, sulfinicacids, alkylsulfuric acids, phosphonic acids, phosphates, and carboxylicacids, as described in, for example, JP-A 60-88942 and JP-A 2-96755.Specific examples of these organic acids include p-toluenesulfonic acid,dodecylbenzenesulfonic acid, p-toluenesulfinic acid, ethylsulfuric acid,phenylphosphonic acid, phenylphosphinic acid, phenyl phosphate, diphenylphosphate, benzoic acid, isophthalic acid, adipic acid, p-toluic acid,3,4-dimethoxybenzoic acid, phthalic acid, terephthalic acid,4-cyclohexene-1,2-dicarboxylic acid, erucic acid, lauric acid,n-undecanoic acid, and ascorbic acid. The amount of the cyclic acidanhydride, phenol, or organic acid contained in the coating ispreferably in the range of 0.05 to 20% by weight, relative to thecoating as a whole.

Blocking Agent

In accordance with a preferred embodiment of the present invention, theblocking agent is added to the developing solution by removing at leasta portion of the precursor wherein the blocking agent of a preferredembodiment of the present invention is present. In this preferredembodiment, the layer including the blocking agent is removed at leastpartially during development, preferably, the blocking agent is presentin the heat-sensitive coating or in the heat-sensitive layer and/or theintermediate layer and/or in a top layer and/or in an optional otherlayer on the back side of the support.

According to a more preferred embodiment, the blocking agent is presentin the heat-sensitive coating or in the heat-sensitive layer and/or theintermediate layer whereby the layer including the blocking agent isremoved at the exposed areas in the developing solution. In this way, itis highly advantageous that the amount of blocking agent added to thedeveloping solution is in correspondence with the amount of precursorsdeveloped. When the precursor has a toplayer which is removed only onthe exposed areas, the blocking agent can also be present in thetoplayer and the addition of blocking agent is also in correspondencewith the exposed areas. In this way, the blocking agent is released inproportion with exposed areas and the amount of blocking agent presentin such an image-wise dissolving coating ranges preferably between 0.01g/m² to 2.5 g/m², more preferably between 0.05 g/m² to 1.5 g/m², mostpreferably between 0.07 g/m² to 1.0 g/m².

According to another preferred embodiment of the present invention, theblocking agent is present in a layer on the back side of the support andthis layer is removed at least partially in the developing solution. Inthis way, the addition of the blocking agent is proportional with thesurface of the precursors which are developed. In an analogous way, theblocking agent can also be present in a top layer which is removed alsoin the non-exposed areas. In this way, the blocking agent is released inproportion with a surface of the precursor and the amount of blockingagent present in such a layer ranges preferably between 0.01 g/m² to 2.0g/m², more preferably between 0.05 g/m² to 1.5 g/m², most preferablybetween 0.07 g/m² to 1.0 g/m².

In order to obtain an optimum blocking activity, it is advantageous tocombine a precursor, having the blocking agent in a coating in a lowerconcentration, preferably between 0.005 and 0.35 g/m², with a developingsolution (or replenisher), having a concentration of the blocking agent,preferably in the range of 0.1 and 3 g/l.

Exposure

The material can be image-wise exposed directly with heat, e.g., by athermal head, or indirectly by infrared light, which is preferablyconverted into heat by an infrared light absorbing compound, which maybe a dye or pigment having an absorption maximum in the infraredwavelength range. The infrared light absorbing dye or pigment ispreferably present in the heat-sensitive coating or the heat-sensitivelayer and typically in a concentration ranging between 0.25 and 10.0 wt.%, more preferably between 0.5 and 7.5 wt. % relative to the coating asa whole. Preferred IR-absorbing compounds are dyes such as cyanine ormerocyanine dyes or pigments such as carbon black. A suitable compoundis the following infrared dye IR-1:

wherein X⁻ is a suitable counter ion such as tosylate.

The heat-sensitive coating, or the heat-sensitive layer and/or theintermediate layer, may further contain an organic dye which absorbsvisible light so that a perceptible image is obtained upon image-wiseexposure and subsequent development. Such a dye is often called contrastdye or indicator dye. Preferably, the dye has a blue color and anabsorption maximum in the wavelength range between 600 nm and 750 nm.Although the dye absorbs visible light, it preferably does not sensitizethe printing plate precursor, i.e., the coating does not become moresoluble in the developer upon exposure to visible light. Suitableexamples of such a contrast dye are the quaternized triarylmethane dyes.

According to a preferred embodiment, the contrast dye is present in theheat-sensitive coating, or the heat-sensitive layer and/or theintermediate layer.

According to a highly preferred embodiment, the infrared light absorbingcompound is concentrated in the heat-sensitive coating or theheat-sensitive layer.

The printing plate precursor of a preferred embodiment of the presentinvention can be exposed to infrared light with LEDs or a laser.Preferably, a laser emitting near infrared light having a wavelength inthe range from about 750 to about 1500 nm is used, such as asemiconductor laser diode, a Nd:YAG or a Nd:YLF laser. The requiredlaser power depends on the sensitivity of the image-recording layer, thepixel dwell time of the laser beam, which is determined by the spotdiameter (typical value of modern plate-setters at 1/e² of maximumintensity: 10-25 μm), the scan speed and the resolution of the exposureapparatus (i.e., the number of addressable pixels per unit of lineardistance, often expressed in dots per inch or dpi; typical value:1,000-4,000 dpi).

Two types of laser-exposure apparatuses are commonly used: internal(ITD) and external drum (XTD) plate-setters. ITD plate-setters forthermal plates are typically characterized by a very high scan speed upto 500 m/sec and may require a laser power of several Watts. XTDplate-setters for thermal plates having a typical laser power from about200 mW to about 1 W operate at a lower scan speed, e.g., from 0.1 to 10m/sec.

The known plate-setters can be used as an off-press exposure apparatus,which offers the benefit of reduced press down-time. XTD plate-setterconfigurations can also be used for on-press exposure, offering thebenefit of immediate registration in a multi-color press. More technicaldetails of on-press exposure apparatuses are described in e.g., U.S.Pat. No. 5,174,205 and U.S. Pat. No. 5,163,368.

In the development step, the non-image areas of the coating are removedby immersion in an aqueous alkaline developer, which may be combinedwith mechanical rubbing, e.g., by a rotating brush. The developerpreferably has a pH above 10, more preferably above 12. The developermay further contain a poly hydroxyl compound such as, e.g., sorbitol,preferably in a concentration of at least 40 g/l, and also apolyethylene oxide containing compound such as, e.g., Supronic B25,commercially available from RODIA, preferably in a concentration of atmost 0.15 g/l.

The development step may be followed by a rinsing step and/or a gummingstep. The gumming step involves post-treatment of the lithographicprinting plate with a gum solution. A gum solution is typically anaqueous liquid which includes one or more surface protective compoundsthat are capable of protecting the lithographic image of a printingplate against contamination or damaging. Suitable examples of suchcompounds are film-forming hydrophilic polymers or surfactants.

The plate precursor can, if required, be post-treated with a suitablecorrecting agent or preservative as known in the art. To increase theresistance of the finished printing plate and hence to extend the runlength, the layer can be briefly heated to elevated temperatures(“baking”). The plate can be dried before baking or is dried during thebaking process itself. During the baking step, the plate can be heatedat a temperature which is higher than the glass transition temperatureof the heat-sensitive coating, e.g., between 100° C. and 230° C. for aperiod of 40 seconds to 5 minutes. Baking can be done in conventionalhot air ovens or by irradiation with lamps emitting in the infrared orultraviolet spectrum. As a result of this baking step, the resistance ofthe printing plate to plate cleaners, correction agents and UV-curableprinting inks increases. Such a thermal post-treatment is described,inter alia, in DE 1,447,963 and GB 1,154,749.

The printing plate thus obtained can be used for conventional, so-calledwet offset printing, in which ink and an aqueous dampening liquid issupplied to the plate. Another suitable printing method uses so-calledsingle-fluid ink without a dampening liquid. Suitable single-fluid inkshave been described in U.S. Pat. No. 4,045,232; U.S. Pat. No. 4,981,517and U.S. Pat. No. 6,140,392. In a preferred embodiment, the single-fluidink includes an ink phase, also called the hydrophobic or oleophilicphase, and a polyol phase as described in WO 00/32705.

EXAMPLES Preparation of Binder-01

In a 250 ml reactor, 162 mmol of Monomer-01, 21.3 g (132 mmol) benzylacrylamide, 0.43 g (6 mmol) acrylic acid and 103 g gamma-butyrolactonewere added and the mixture was heated to 140° C., while stirring at 200rpm. A constant flow of nitrogen was put over the reactor. Afterdissolution of all the components, the reactor was cooled to 100° C.0.35 ml Trigonox DC50, commercially available from AKZO NOBEL, was addedfollowed by the addition of 1.39 ml Trigonox 141, commercially availablefrom AKZO NOBEL, in 3.43 ml butyrolactone. The polymerization wasstarted and the reactor was heated to 140° C. over 2 hours while dosing1.75 ml Trigonox DC50. The mixture was stirred at 400 rpm and thepolymerization was allowed to continue for 2 hours at 140° C. Thereaction mixture was cooled to 120° C. and the stirrer speed wasenhanced to 500 rpm. 85.7 ml 1-methoxy-2-propanol was added and thereaction mixture was allowed to cool down to room temperature.

Binder-01 was analyzed with ¹H-NMR-spectroscopy and size exclusionchromatography, using dimethyl acetamide/0.21% LiCl as eluent on a 3×mixed-B column and relative to polystyrene standards.

M_(n) M_(w) PD Binder-01 23500 67000 2.84

The reaction mixture was cooled to 40° C. and the resulting 25 weight %polymer solution was collected in a drum.

Preparation of the Lithographic Support

A 0.30 mm thick aluminum foil was degreased by immersing the foil in anaqueous solution containing 34 g/l of sodium hydroxide at 70° C. for 6seconds and rinsed with demineralized water for 3.6 seconds. The foilwas then electrochemically grained for 8 seconds using an alternatingcurrent in an aqueous solution containing 15 g/l HCl, 15 g/l SO₄ ²⁻ ionsand 5 g/l Al³⁺ at a temperature of 37° C. and a current density of 100A/dm². The aluminum foil was then desmutted by etching with an aqueoussolution containing 145 g/l of sulfuric acid at 80° C. for 5 seconds andrinsed with demineralized water for 4 seconds. The foil was subsequentlysubjected to anodic oxidation for 10 seconds in an aqueous solutioncontaining 145 g/l of sulfuric acid at a temperature of 57° C. and acurrent density of 25 A/dm², then washed with demineralized water for 7seconds and post-treated for 4 seconds with a solution containing 2.2g/l of polyvinylphosphonic acid at 70° C., rinsed with demineralizedwater for 3.5 seconds and dried at 120° C. for 7 seconds.

The support thus obtained was characterized by a surface roughness Ra of0.35-0.40 μm (measured with interferometyer NT1100) and an anodic weightof 3.0 g/m².

Preparation of the Printing Plate Precursor PPP-01

The PPP-01 was produced by first applying a first coating layer definedin Table 1 onto the above described lithographic support. The coatingwas applied at a wet coating thickness of 20 μm and then dried at 135°C.

TABLE 1 Composition of the Solution of the First Coating Layer Amount ofproduct INGREDIENTS (g) Dowanol PM (1) 351.54 THF (2) 1698.99 Binder-01(25% by weight) (3) 661.86 Crystal Violet (1% by weight) (4) 253.77Tegoglide 410 (1% by weight) (5) 33.84 (1) Dowanol PM is1-methoxy-2-propanol, commercially available from DOW CHEMICAL Company.(2) THF is tetrahydrofuran. (3) Binder-01, preparation see above. (4)Crystal Violet, commercially available from CIBA-GEIGY. (5) TEGOGLIDE410 is a copolymer of polysiloxane and poly(alkylene oxide),commercially available from TEGO CHEMIE SERVICE GmbH.

On the first coated layer, a second layer as defined in Table 2 wascoated at a wet coating thickness of 25 μm and dried at 135° C.

TABLE 2 Composition of the Solution of the Second Coating Layer Amountof product INGREDIENTS (g) Dowanol PM (1) 600.73 Alnovol SPN452 (40% byweight) (2) 132.07 TMCA (10% by weight) (3) 68.20 SOO94 (4) 2.74 CrystalViolet (1% by weight) (5) 80.23 Tegowet 265 (1% by weight) (6) 11.23Tegoglide 410 (1% by weight) (7) 36.90 Butanone 867.91 (1) See Table 1.(2) Alnovol SPN452 is a novolac solution, 40.5% by weight in Dowanol PM,commercially available from CLARIANT. (3) TMCA is 3,4,5-trimethoxycinnamic acid. (4) SOO94 is an IR absorbing cyanine dye, commerciallyavailable from FEW CHEMICALS; the chemical structure of SOO94 is equalto IR-1 (5) See Table 1. (6) Tegowet 265 is a copolymer of polysiloxaneand poly(alkylene oxide), commercially available from TEGO CHEMIESERVICE GmbH. (7) See Table 1.Imaging and Processing of the Printing Plate Precursor PPP-01 withDEV-01 to DEV-03

The printing plate precursor PPP-01 was exposed with a Creo Trendsetter3244 (plate-setter, trademark from Creo, Burnaby, Canada), operating at150 rpm and varying energy densities up to 200 mJ/cm².

After exposure, the plate was processed with the developing solutionsDEV-01 to DEV-03 as defined in Table 4.

TABLE 4 Composition of Developing Solutions DEV-01 to DEV-03 DEV-01DEV-02 DEV-03 INGREDIENTS (g) (g) (g) Na-metasilicate (1) 88 88 88Crafol AP261 (2) 8.83 8.83 8.83 Synperonic T304 (3) 4.4 4.4 4.4 Block-010.175 Block-03 0.31 Water until 1000 1000 1000 (1) Na-metasilicate issodium metasilicate pentahydrate, commercially available from SILMACO NV(2) Crafol AP261 is alkylether sodium salt, commercially available fromCOGNIS (3) Synperonic T304 is a block-co-polymer of polyethylene oxide(=PEO) and polypropylene oxide (=PPO) attached to ethylenediamine (=EDA)in a ratio EDA/PEO/PPO of 1/15/14 and having a mean molecular weight of1600, commercially available from UNIQEMA.

In these experiments, the precursor was exposed at the Right Exposure,hereinafter also referred to as RE. The RE is defined as the exposureenergy at which a dot coverage on the plate for a 1×1 checkerboard andfor a 8×8 checkerboard matches 50%. The dot coverage was measured with aGretagMacbeth D19C densitometer, commercially available fromGretag-Macbeth AG, with the uncoated support as reference.

The development latitude was determined by developing a 1×1 checkerboardat different developing times. The Right Developing Time, hereinafteralso referred to as RDT, is defined whereby the optical density,hereinafter also referred to as OD, on the plate match a 50% dotcoverage, measured with a densitometer as described above. (A 50% dotcoverage corresponds with an OD of approximately 0.3; the experimentallymeasured values are indicated in Table 5). The development latitude wasmeasured by the difference between the optical density of a 1×1checkerboard, developed at a shorter (e.g., −3 seconds) or longer (e.g.,+2, +5 or +10 seconds) developing time, and the optical density of a 1×1checkerboard, developed at the RDT. The lower the absolute value of thisdifference in OD, the more efficient the additive is working as ablocking agent to reduce the dissolution kinetic of this coating and themore the development latitude is improved.

The results are summarized in Table 5.

TABLE 5 Results of Developing Latitude Comparative Inventive InventiveExample 1 Example 1 Example 2 Precursor PPP-01 PPP-01 PPP-01 Developingsolution DEV-01 DEV-02 DEV-03 Right developing time for 1x1 22 s 22 s 27s screen pattern (RDT) (seconds) OD_((1x1)) at RDT 0.30 0.32 0.29[(OD_((1x1)) at RDT + 2 s) − −0.11 −0.05 (OD_((1x1)) at RDT)][(OD_((1x1)) at RDT + 5 s) − −0.14 −0.06 −0.07 (OD_((1x1)) at RDT)][(OD_((1x1)) at RDT + 10 s) − −0.24 −0.10 −0.13 (OD_((1x1)) at RDT)][(OD_((1x1)) at RDT − 3 s) − +0.09 +0.03 +0.08 (OD_((1x1)) at RDT)]

The results in Table 5 demonstrate that the improved developmentlatitude for the Inventive Examples 1 and 2 including a blocking agentaccording to a preferred embodiment of the present invention in thedeveloping solution in comparison with the Comparative Example 1.

Imaging and Processing of the Printing Plate Precursor PPP-01 withDEV-04 to DEV-07

The printing plate precursor PPP-01 was exposed with a Creo Trendsetter3244 (plate-setter, trademark from Creo, Burnaby, Canada), operating at150 rpm and an energy density of 100, 110 and 120 mJ/cm².

After exposure, the plate was processed with the developing solutions ata temperature of 25° C. for 15 seconds for and for 16 seconds for DEV-05to DEV-07. The composition of the developing solutions are defined inTable 6.

TABLE 6 Composition of Developing Solutions DEV-04 to DEV-07 DEV-04DEV-05 DEV-06 DEV-07 INGREDIENTS (g) (g) (g) (g) Na-metasilicate (1) 177177 177 177 Crafol AP261 (2) 22.3 22.3 22.3 22.3 Compound-01 0.89Block-01 0.356 Block-05 0.89 Water 1780 1780 1780 1780 (1) and (2) seeTable 4.

The dot coverages of a 8×8 checkerboard, exposed at these three exposureenergies, were measured with a GretagMacbeth D19C densitometer with theuncoated support as reference, as described above.

The exposure latitude is determined by the difference between the OD ofthe 8×8 checkerboard at each exposure energy. The lower this differencein OD, the more efficient of the additive is working as a blocking agentto reduce the dissolution kinetic of this coating and the more theexposure latitude is improved.

The results are summarized in Table 7.

TABLE 7 Results of Exposure Latitude Exposure Developing DevelopingEnergy time OD Precursor solution (mJ/cm²) (seconds) (8x8) ComparativePPP-01 DEV-04 100 15 s 0.180 Example 2 110 15 s 0.137 120 15 s 0.095Comparative PPP-01 DEV-05 100 16 s 0.204 Example 3 110 16 s 0.089 120 16s 0.012 Inventive PPP-01 DEV-06 100 16 s 0.300 Example 3 110 16 s 0.301120 16 s 0.293 Inventive PPP-01 DEV-07 100 16 s 0.340 Example 4 110 16 s0.330 120 16 s 0.313

The results in Table 7 demonstrate that the improved exposure latitudefor the Inventive Examples 3 and 4 including a blocking agent accordingto a preferred embodiment of the present invention in the developingsolution DEV-06 and DEV-07.

The developing solutions DEV-04 and DEV-05 in the Comparative Examples 2and 3 include no blocking agent and a blocking agent of the prior artrespectively, whereby these developing solutions behave a too strongdeveloping property resulting in an OD<0.3 for a 8×8 checkerboard. Thisdrop in OD is much higher with increasing exposure energy. This meansthat the exposure latitude for these developing solutions is very poorin comparison with the developing solutions of the preferred embodimentsof the present invention whereby the change in OD at different exposureenergies is very small, resulting in a high exposure latitude.

Preparation of the Printing Plate Precursor PPP-02

The PPP-02 was produced by applying a coating layer defined in Table 8onto the above described lithographic support. The solvent used to applythe coating is a mixture of 17% by volume of Dowanol PM and 83% byvolume of tetrahydrofuran. The coating was applied at a wet coatingthickness of 20 μm and then dried at 135° C.

TABLE 8 Composition of the Coating Layer Amount of product INGREDIENTS(g/m²) Binder-01 (25% by weight) (1) 1.00 Crystal Violet (1% by weight)(2) 0.019 Tegoglide 410 (1% by weight) (3) 0.0025 Total dry coatingweight (g/m²) 1.02 (1) to (3) see previous tables.

Processing of the Printing Plate Precursor PPP-02 in DEV-Reference andDEV-08 to DEV-22

The printing plate precursor PPP-02 includes the coating layer asdefined in Table 8 and this layer has an analogous composition as thefirst coating layer of PPP-01. This layer is soluble in an alkalinesolution and is used as a model for testing the efficiency of theblocking agents to reduce the dissolution kinetic of non-exposed areas.Therefore, the precursor PPP-02 was processed, without previously beenexposed to IR-laser or heat, in the developing solutions as mentioned inTable 9 and 10 with a dwell time of 20 seconds at a temperature of 25°C. DEV-Reference is a developing solution without addition of a blockingagent or another compound; DEV-08 to DEV-18 are developing solutionsincluding a blocking agent of preferred embodiments of the presentinvention; and DEV-19 to DEV-22 are developing solutions includinganother additive compound as defined in Table 9 and 10.

TABLE 9 Composition of the Developing Solutions DEV-Reference and DEV-08to DEV-22 DEV- DEV-08 to DEV-18 to Reference DEV-17 DEV-22 INGREDIENTS(g) (g) (g) Na-glucoheptonate (1) 5 5 5 Na-metasilicate (2) 102 102 102Na-silicate solution (3) 10 10 10 Variquat cc 9NS (4) 0.044 0.044 0.044Triton H-66 (5) 5.8 5.8 5.8 Synperonic T304 (6) 0.141 0.141 0.141 ablocking agent added as 0.01 mol defined in Table 10 a compound added asdefined 0.01 mol in Table 10 Water until 1000 1000 1000 (1)Na-glucoheptonate is glucoheptonate sodium salt (2) See previous tables(3) Variquat cc 9NS is a cationic surfactant, commercially availablefrom GOLDSCHMIDT (4) Triton H-66 is an anionic surfactant, commerciallyavailable from SEPULCHRE (5) See previous tables.

After processing, the OD is measured with a GretagMacbeth D19Cdensitometer with the uncoated support as reference, as described above.The difference between the OD of the plate PPP-02, developed with eachof the developing solutions DEV-08 to DEV-22, and the OD of the platePPP-02, developed with DEV-Reference, were calculated. The higher thevalue of this difference in OD, the more efficient the additive isworking as a blocking agent to reduce the dissolution kinetic of thiscoating.

The blocking efficiency of the different compounds was rated by thedifference in OD:

Code 0: difference in OD<0.15, means a very poor blocking effect,Code 1: difference in OD>0.15 and <0.60, means a moderate blockingeffect,Code 2: difference in OD≧0.60 and <1.00, means a good blocking effect,Code 3: difference in OD>1.00, means a high blocking effect.

The results are summarized in Table 10.

TABLE 10 Results of Blocking Efficiency Additive in Code for Developingdeveloping blocking Precursor solution solution efficiency InventivePPP-02 DEV-08 Block-01 2 Example 5 Inventive PPP-02 DEV-09 Block-02 2Example 6 Inventive PPP-02 DEV-10 Block-03 3 Example 7 Inventive PPP-02DEV-11 Block-04 3 Example 8 Inventive PPP-02 DEV-12 Block-05 2 Example 9Inventive PPP-02 DEV-13 Block-06 1 Example 10 Inventive PPP-02 DEV-14Block-07 1 Example 11 Inventive PPP-02 DEV-15 Block-08 3 Example 12Inventive PPP-02 DEV-16 Block-09 3 Example 13 Inventive PPP-02 DEV-17Block-10 2 Example 14 Comparative PPP-02 DEV-18 Compound-02 0 Example 5Comparative PPP-02 DEV-19 Compound-03 0 Example 6 Comparative PPP-02DEV-20 Compound-04 0 Example 7 Comparative PPP-02 DEV-21 Compound-05 0Example 8 Comparative PPP-02 DEV-22 Compound-06 0 Example 9

The results in Table 10 demonstrate that, in the Inventive Examples 5 to14, the developers DEV-08 to DEV-17 including a blocking agent of apreferred embodiment of the present invention exhibit an improvedefficiency in reducing the dissolution kinetic of this coating. In theComparative Examples to 9, the developers DEV-18 to DEV-22, including acompound of the prior art, exhibit a poor blocking effect.

Preparation of the Printing Plate Precursors PPP-03 to PPP-07

The PPP-03 to PPP-07 were produced by first applying a first coatinglayer defined in Table 11 onto the above described lithographic support.The coating was applied at a wet coating thickness of 20 μm and thendried at 135° C. The dry coating weight amounts to 1.02 g/m².

TABLE 11 Composition of the Solution of the First Coating Layer AmountAmount Amount of Amount of of Amount of of product product productproduct product for for for for for PPP-03 PPP-04 PPP-05 PPP-06 PPP-07INGREDIENTS (g) (g) (g) (g) (g) Dowanol PM (1) 160.74 160.45 160.45160.45 160.45 THF (2) 536.04 535.96 535.96 535.96 535.96 Binder-01211.37 211.62 211.62 211.62 211.62 (25 wt. %) (3) Block-04 1.35 Block-111.35 Block-03 1.35 Block-01 1.35 Crystal 81.05 81.14 81.14 81.14 81.14Violet (1 wt. %) (4) Tegoglide 410 10.81 10.82 10.82 10.82 10.82 (1 wt.%) (5) (1) to (5) see previous tables.

On the first coated layer, a second layer as defined in Table 12 wascoated at a wet coating thickness of 25 μm and dried at 135° C. The drycoating weight amounts to 0.80 g/m².

TABLE 12 Composition of the Solution of Second Coating Layer Amount ofproduct for PPP-03 to PPP-07 INGREDIENTS (g) Dowanol PM (1) 235.0Alnovol SPN452 (40% by weight) (2) 117.11 TMCA (10% by weight) (3) 60.34SOO94 (4) 2.41 Crystal Violet (1% by weight) (5) 70.99 Tegowet 265 (1%by weight) (6) 9.94 Tegoglide 410 (1% by weight) (7) 32.65 Butanone471.55 (1) to (5) see previous tables.

Imaging and Processing of Printing Plate Precursor PPP-03 to PPP-07

The printing plate precursors PPP-03 to PPP-07 were, in a firstexperiment, exposed with a Creo Trendsetter 3244 (plate-setter,trademark from Creo, Burnaby, Canada), operating at 150 rpm at the RightExposure (RE) as defined above and developed with DEV-01 as definedabove in Table 4.

In a second experiment, the printing plate precursors PPP-03 to PPP-07were exposed by a 1×1 checkerboard at an exposure energy which is 20%lower than the RE value as determined above and, also, at an exposureenergy which is 20% higher than the RE value. After developing, the dotcoverage for the under-exposure by 20% and for the over-exposure by 20%was measured by the OD as defined above. The exposure latitude wasdetermined by the difference between the dot coverage by the 20%under-exposure and the dot coverage by the 20% over-exposure. The lowerthe absolute value of this difference, the more efficiently thedissolution kinetic of the coating is reduced and the more the exposurelatitude is improved.

The results are summarized in Table 13.

TABLE 13 Results of Exposure Latitude RE-value [Dotcoverage_(at RE−20%)] − EXAMPLES PPP-type (mJ/cm²) [Dotcoverage_(at RE+20%)] Comparative PPP-03 89 19 Example 10 InventivePPP-04 124 13 Example 15 Inventive PPP-05 132 12 Example 16 InventivePPP-06 110 8 Example 17 Inventive PPP-07 121 15 Example 18

The results in Table 13 demonstrate an improved exposure latitude forthe Inventive Examples 15 to 18, including a blocking agent according toa preferred embodiment of the present invention, whereby the differencebetween the dot coverage by the 20% under-exposure and the dot coverageby the 20% over-exposure is lower than in the Comparative Example 10.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1-11. (canceled)
 12. A method for making a lithographic printing platecomprising the steps of: providing a heat-sensitive lithographicprinting plate precursor including a support having a hydrophilicsurface or which is provided with a hydrophilic layer, and aheat-sensitive coating on the support; image-wise exposing the precursorwith IR-radiation or heat; and developing the image-wise exposedprecursor with an alkaline developing solution including a compoundhaving at least two onium groups; wherein the compound having at leasttwo onium groups has a structure according to Formula I, II, or III:

Z^(a)-L-Z^(b),  Formula III Q is a divalent group when e and f are 0, atrivalent group when the sum of e and f is 1, or a tetravalent groupwhen e and f are both 1; Z^(a) to Z^(d) independently are onium groups;L and L^(a) to L^(d) independently are linking groups; and Z^(x)-L^(x)-represents a repeating unit wherein Z^(x) and L^(x) representrespectively an onium group and a linking group for each x-value; a, b,c, d, e, and f independently are 0 or 1; and x is an integer rangingbetween 1 and
 10. 13. A method according to claim 12, wherein thelinking group is selected from the group consisting of a linear,branched, or cyclic alkylene group; an arylene group; anarylene-alkylene group; an oxy-alkylene group; an oxy-arylene group; anoxy-heteroarylene group; and a combination of two or more of thesegroups.
 14. A method according to claim 12, wherein the onium group isselected from the group consisting of primary amine salts, secondaryamine salts, tertiary amine salts, quaternary ammonium salts,phosphonium salts, and sulphonium salts.
 15. A method according to claim12, wherein the precursor includes a compound having a structureaccording to Formula I, II, or III, and during the developing step, atleast a portion of the compound is removed from the precursor.
 16. Amethod according to claim 12, wherein during or after the developingstep, a replenishing solution including a compound having a structureaccording to Formula I, II, or III is added to the developing solution.17. A method according to claim 12, wherein the alkaline developingsolution including the compound having a structure according to FormulaI, II, or III further includes a silicate or metasilicate.
 18. Anaqueous alkaline developing solution or replenishing solutioncomprising: an alkaline agent and a compound having a structureaccording to Formula I, II, or III:


19. A heat-sensitive lithographic printing plate precursor comprising: asupport having a hydrophilic surface or which is provided with ahydrophilic layer; and on the support, a heat-sensitive coatingincluding a compound having a structure according to Formula I, II, orIII: